This invention is useful for indicating the direction of a steerable wheel in a vehicle, and the invention is particularly useful for that purpose in an industrial truck of the kind which has a steerable wheel which can be turned through a steering arc of as much as 180 degrees.
The invention is especially useful for industrial forklift trucks which are often battery powered, and which are used for bulk materials handling.
Some industrial forklift trucks are especially adapted for operation in very narrow aisles in materials storage warehouses. These trucks commonly employ three wheels, only one of which is steerable, and very frequently the drive motor is connected to drive the steerable wheel, so that the steerable wheel is the only traction wheel. Some design variations may include a fourth wheel which is a freely turnable idler wheel, but which is not a traction wheel and is not actually steerable, or a fourth wheel which is steerable. In such a truck design, in order to enhance maneuverability, the steerable wheel can be turned through an angle of essentially 180 degrees, and the traction motor may be reversed so as to provide for a full 360 degree selection of the steerable wheel travel direction.
The steerable wheel is usually substantially completely hidden beneath the structure of the truck, and the operator frequently stops the truck to pick up or discharge a load. The operator must then rely upon his memory to determine how the truck will move in response to the position of the steerable wheel after stopping to load or unload, or after having taken a break from operation of the truck for any purpose. It is important for the operator to know which direction the steerable wheel is going to travel when he again starts to move the truck because the direction of travel can be quite critical in a narrow aisle in avoiding accidents and damage to stored goods, and in promoting efficient operation. Speed of manipulation is important in promoting total productivity in shifting and moving and storing loads of materials.
Accordingly, there is a real need for an accurate and highly visible and usable steerable wheel travel direction indicator for industrial forklift trucks.
This need has been recognized, and at least one prior attempt has been made to fulfill the need. For instance, see the Houseman et al U.S. Pat. No. 3,900,831 for an "Operation Lamp and Steer Indicator" issued August 1985 and assigned to the Eaton Corporation of Ceveland, Ohio. That patent discloses a steering indicator which is applied to a three wheel forklift truck of the kind mentioned above, and which relies upon a simple mechanical coupling between the steering spindle of the steerable wheel and a rotatable dial type of indicator which carries a rotatable indicator lamp, the indicator lamp serving to indicate the direction of the steerable wheel. That mechanism appears to be effective for its intended purpose. However, the mechanism is quite bulky, and tends to crowd the space within the housing of the truck. Such space is at a premium because the truck is very compact so as to be accommodated easily in narrow aisle spaces. Also, the indicator of the Houseman patent only indicates steerable wheel travel direction for forward directions of wheel travel, and does not accommodate for reverse directions of wheel travel. Furthermore, as pointed out in the Houseman patent, a steerable wheel travel direction indicator is especially important in so-called "order picking" trucks where the operator is positioned upon and controls the vehicle from a platform which travels up and down with the forklift, and which may be located high above the power unit of the vehicle at a time when the vehicle is to be moved. From the standpoint of operator safety, as well as efficient operation, it is important that when the operator platform is located in the elevated position, the operator should not be subjected to movement of the vehicle in an unexpected direction. Thus, it is especially important for the operator to have an indicator for the steerable wheel travel direction in such a vehicle when the operator is in the elevated position. While the Houseman patent is especially directed to that problem, it does not solve that problem particularly effectively, since the operator must look down from his elevated position to the Houseman direction indicator device, which is not elevated with him, and which may be difficult to read with accuracy, particularly if the operator is not farsighted. Accordingly, it is an important object of the present invention to provide an improved steerable wheel travel direction indicator which is very compact, and which is very accurate and effective.
Another object of the invention is to provide an improved steerable wheel travel direction indicator which can be installed at any convenient position for convenient viewing by the operator, such as on an operator platform which is adjustable in height.
Another object of the invention is to provide an improved steerable wheel travel direction indicator which is capable of separately indicating wheel travel direction in either forward steerable directions or reverse steerable directions.
Steerable wheel travel direction indicators have also been proposed for automotive vehicles. One such system is disclosed, for instance, in U.S. Pat. No. 3,673,561 issued to Harry Bronstein on June 27, 1972 for a "Steering Indicator". That steering indicator employs a potentiometer which is mechanically coupled to the steering gear to be positioned according to the direction of the wheels. An electromagnetic meter is connected to receive the signal from the potentiometer and to provide a visual indication of wheel position. In such an apparatus it is difficult to achieve and maintain an accurate calibration. Furthermore, for a very wide angle of wheel direction change, it is difficult to provide a meter with sufficient angular travel to match the angular change in wheel direction.
Accordingly, it is another important object of the present invention to provide an improved steerable wheel travel direction indicator which is extremely accurate, which maintains its calibration, and which is simple and inexpensive and shock resistant.
It is another object of the invention to provide a steerable wheel travel direction indicator which is capable of indicating travel direction over a wide angle of direction change.
Still another prior automotive wheel direction indicator invention is disclosed and described in U.S. Pat. No. 4,342,279 issued Aug. 3, 1982 to Seko et al, for a "Device for Detecting Steering Angle and Direction", and assigned to Nissan Motor Company Limited. The system diclosed in that patent employs directional electromechanical switch elements which are caused to provide pulse signals on different signal lines for left or right turnng movement respectively, and the resultant count is stored in a counter indicator M, the steering angle being registered digitally in the indicator M. The type of display provided by the indicator M is not described.
While this system would appear to be accurate, within the limitations of the counter indicator, and the mechanism limitations, the one-way electromechanical switch elements may be subject to wear and possible erratic operation, and the digital display may be difficult to interpret.
Accordingly, it is another object of the present invention to provide an improved steerable travel direction indicator providing a display which is very easily interpreted, and providing for reliable and trouble free operation.
Further objects and advantages of the invention will be apparent from the following description and the accompanying drawings.